Radio communication device and constellation control method

ABSTRACT

A base station is provided for receiving an acknowledgement or negative acknowledgement (ACK/NACK) signal, including a transmitting unit configured to transmit a control signal using one or a plurality of CCE(s). The base station also includes a receiving unit configured to receive an ACK/NACK signal, the ACK/NACK signal being multiplied by an orthogonal sequence, by a sequence defined by a cyclic shift, and by either a first value or a second value, wherein the first value rotates a constellation of the ACK/NACK signal by 0 degrees and the second value rotates the constellation of the ACK/NACK signal by N degrees, which is different from 0 degrees.

TECHNICAL FIELD

The present invention relates to a radio communication apparatus andconstellation control method.

DESCRIPTION OF THE RELATED ART

In mobile communication, ARQ (Automatic Repeat Request) is applied todownlink data from a radio communication base station apparatus(hereinafter abbreviated to “base station”) to radio communicationmobile station apparatuses (hereinafter abbreviated to “mobilestations”). That is, mobile stations feed back response signalsrepresenting error detection results of downlink data, to the basestation. Mobile stations perform a CRC (Cyclic Redundancy Check) checkof downlink data, and, if CRC=OK is found (i.e., if no error is found),feed back an ACK (ACKnowledgement), and, if CRC=NG is found (i.e., iferror is found), feed back a NACK (Negative ACKnowledgement), as aresponse signal to the base station. These response signals aretransmitted to the base station using uplink control channels such as aPUCCH (Physical Uplink Control CHannel).

Also, the base station transmits control information for carryingresource allocation results of downlink data, to mobile stations. Thiscontrol information is transmitted to the mobile stations using downlinkcontrol channels such as L1/L2 CCH's (L1/L2 Control CHannels). EachL1/L2 CCH occupies one or a plurality of CCE's (Control ChannelElements) based on the coding rate of control information. For example,when an L1/L2 CCH for carrying control information coded by a rate of ⅔occupies one CCE, an L1/L2 CCH for carrying control information coded bya rate of ⅓ occupies two CCE's, an L1/L2 CCH for carrying controlinformation coded by a rate of ⅙ occupies four CCE's and an L1/L2 CCHfor carrying control information coded by a rate of 1/12 occupies eightCCE's. Also, when one L1/L2 occupies a plurality of CCE's, the CCE'soccupied by that one L1/L2 CCH are consecutive. The base stationgenerates an L1/L2 CCH on a per mobile station basis, assigns CCE's tobe occupied by L1/L2 CCH's based on the number of CCE's required bycontrol information, and maps the control information on physicalresources corresponding to the assigned CCE's and transmits the controlinformation.

Also, studies are underway to map between CCE's and PUCCH's on aone-to-one basis, to use downlink communication resources efficientlywithout signaling from a base station to mobile stations for reportingthe PUCCH's to be used for transmission of response signals (seeNon-Patent Document 1). According to this mapping, each mobile stationcan decide the PUCCH to use to transmit response signals from the mobilestation, from the CCE's corresponding to physical resources on whichcontrol information for the mobile station is mapped. Therefore, eachmobile station maps a response signal from the mobile station on aphysical resource, based on the CCE corresponding to a physical resourceon which control information directed to the mobile station is mapped.For example, when a CCE corresponding to a physical resource on whichcontrol information directed to the mobile station is mapped, is CCE #0,the mobile station decides PUCCH #0 associated with CCE #0 as the PUCCHfor the mobile station. Also, for example, when CCE's corresponding tophysical resources on which control information directed to the mobilestation is mapped are CCE #0 to CCE #3, the mobile station decides PUCCH#0 associated with CCE #0, which is the smallest number in CCE #0 to CCE#3, as the PUCCH for the mobile station, and, when CCE's correspondingto physical resources on which control information directed to themobile station is mapped are CCE #4 to CCE #7, the mobile stationdecides PUCCH #4 associated with CCE #4, which is the smallest number inCCE #4 to CCE #7, as the PUCCH for the mobile station.

Also, as shown in FIG. 1, studies are underway to performcode-multiplexing by spreading a plurality of response signals from aplurality of mobile stations using ZAC (Zero Auto Correlation) sequencesand Walsh sequences (see Non-Patent Document 2). In FIG. 1, [W₀, W₁, W₂,W₃] represents a Walsh sequence with a sequence length of 4. As shown inFIG. 1, in a mobile station, first, a response signal of ACK or NACK issubject to first spreading by a ZAC sequence (with a sequence length of12) in the frequency domain. Next, the response signal subjected tofirst spreading is subject to an IFFT (Inverse Fast Fourier Transform)in association with W₀ to W₃. The response signal spread in thefrequency domain by a ZAC sequence with a sequence length of 12 istransformed to a ZAC sequence with a sequence length of 12 in the timedomain by this IFFT. Then, the signal subjected to the IFFT is subjectto second spreading using a Walsh sequence (with a sequence length of4). That is, one response signal is allocated to each of four SC-FDMA(Single Carrier-Frequency Division Multiple Access) symbols S₀ to S₃.Similarly, response signals of other mobile stations are spread usingZAC sequences and Walsh sequences. Here, different mobile stations useZAC sequences of different cyclic shift values in the time domain (i.e.,in the cyclic shift axis) or different Walsh sequences. Here, thesequence length of ZAC sequences in the time domain is 12, so that it ispossible to use twelve ZAC sequences of cyclic shift values “0” to “11,”generated from the same ZAC sequence. Also, the sequence length of Walshsequences is 4, so that it is possible to use four different Walshsequences. Therefore, in an ideal communication environment, it ispossible to code-multiplex maximum forty-eight (12×4) response signalsfrom mobile stations.

Also, as shown in FIG. 1, studies are underway to code-multiplex aplurality of reference signals (e.g., pilot signals) from a plurality ofmobile stations (see Non-Patent Document 2). As shown in FIG. 1, in thecase of generating three symbols of reference signals R₀, R₁ and R₂,similar to the case of response signals, first, the reference signalsare subject to first spreading in the frequency domain by a sequencehaving characteristics of a ZAC sequence (with a sequence length of 12)in the time domain. Next, the reference signals subjected to firstspreading are subject to an IFFT in association with orthogonalsequences with a sequence length of 3, [F₀, F₁, F₂], such as a Fouriersequence. The reference signals spread in the frequency domain areconverted by this IFFT to ZAC sequences with a sequence length of 12 inthe time domain. Further, these signals subjected to IFFT are subject tosecond spreading using orthogonal sequences [F₀, F₁, F₂]. That is, onereference signal is allocated to three SC-FDMA symbols R₀, R₁ and R₂.Similarly, other mobile stations allocate one reference signal to threesymbols R₀, R₁ and R₂. Here, different mobile stations use ZAC sequencesof different cyclic shift values in the time domain or differentorthogonal sequences. Here, the sequence length of ZAC sequences in thetime domain is 12, so that it is possible to use twelve ZAC sequences ofcyclic shift values “0” to “11,” generated from the same ZAC sequence.Also, the sequence length of an orthogonal sequence is 3, so that it ispossible to use three different orthogonal sequences. Therefore, in anideal communication environment, it is possible to code-multiplexmaximum thirty-six (12×3) reference signals from mobile stations.

As shown in FIG. 1, seven symbols of S₀, S₁, R₀, R₁, R₂, S₂ and S₃ formone slot.

Here, there is substantially no cross correlation between ZAC sequencesof different cyclic shift values generated from the same ZAC sequence.Therefore, in an ideal communication environment, a plurality ofresponse signals subjected to spreading and code-multiplexing by ZACsequences of different cyclic shift values (0 to 11), can be separatedin the time domain substantially without inter-code interference, bycorrelation processing in the base station.

However, due to an influence of, for example, transmission timingdifference in mobile stations and multipath delayed waves, a pluralityof response signals from a plurality of mobile stations do not alwaysarrive at a base station at the same time. For example, if thetransmission timing of a response signal spread by the ZAC sequence ofcyclic shift value “0” is delayed from the correct transmission timing,the correlation peak of the ZAC sequence of cyclic shift value “0” mayappear in the detection window for the ZAC sequence of cyclic shiftvalue “1.” Further, if a response signal spread by the ZAC sequence ofcyclic shift value “0” has a delay wave, an interference leakage due tothe delayed wave may appear in the detection window for the ZAC sequenceof cyclic shift value “1.” That is, in these cases, the ZAC sequence ofcyclic shift value “1” is interfered with by the ZAC sequence of cyclicshift value “0.” On the other hand, if the transmission timing of aresponse signal spread by the ZAC sequence of cyclic shift value “1” isearlier than the correct transmission timing, the correlation peak ofthe ZAC sequence of cyclic shift value “1” may appear in the detectionwindow for the ZAC sequence of cyclic shift value “0.” That is, in thiscase, the ZAC sequence of cyclic shift value “0” is interfered with bythe ZAC sequence of cyclic shift value “1.” Therefore, in these cases,the separation performance degrades between a response signal spread bythe ZAC sequence of cyclic shift value “0” and a response signal spreadby the ZAC sequence of cyclic shift value “1.” That is, if ZAC sequencesof adjacent cyclic shift values are used, the separation performance ofresponse signals may degrade.

Therefore, up until now, if a plurality of response signals arecode-multiplexed by spreading with ZAC sequences, a sufficient cyclicshift value difference (i.e., cyclic shift interval) is provided betweenthe ZAC sequences, such that inter-code interference is not causedbetween the ZAC sequences. For example, when the difference betweencyclic shift values of ZAC sequences is 2, only six ZAC sequences ofcyclic shift values “0,” “2,” “4,” “6,” “8” and “10” or cyclic shiftvalues “1,” “3,” “5,” “7,” “9” and “11” amongst twelve ZAC sequences ofcyclic shift values “0” to “12,” are used in first spreading of responsesignals. Therefore, if a Walsh sequence with a sequence length of 4 isused in second spreading of response signals, it is possible tocode-multiplex maximum twenty-four (6×4) response signals from mobilestations.

However, as shown in FIG. 1, the sequence length of an orthogonalsequence used to spread reference signals is 3, and therefore only threedifferent orthogonal sequences can be used to spread reference signals.Consequently, when a plurality of response signals are separated usingthe reference signals shown in FIG. 1, only maximum eighteen (6×3)response signals from mobile stations can be code-multiplexed. That is,three Walsh sequences are required amongst four Walsh sequences with asequence length of 4, and therefore one Walsh sequence is not used.

Also, the 1 SC-FDMA symbol shown in FIG. 1 may be referred to as “1 LB(Long Block).” Therefore, a spreading code sequence that is used inspreading in symbol units or LB units, is referred to as a “block-wisespreading code sequence.”

Also, studies are underway to define eighteen PUCCH's as shown in FIG.2. Normally, the orthogonality of response signals does not collapsebetween mobile stations using different block-wise spreading codesequences, as long as the mobile stations do not move fast. But,especially if there is a large difference of received power betweenresponse signals from a plurality of mobile stations at a base station,one response signal may be interfered with by another response signalbetween mobile stations using the same block-wise spreading codesequence. For example, in FIG. 2, a response signal using PUCCH #1(cyclic shift value=2) may be interfered with by a response signal usingPUCCH #0 (cyclic shift value=0).

Also, studies are underway to use the constellation shown in FIG. 3 whenBPSK is used as the modulation scheme for response signals, and theconstellation shown in FIG. 4 when QPSK is used as the modulation schemefor response signals (see Non-Patent Document 3).

-   Non-Patent Document 1: NTT DoCoMo, Fujitsu, Mitsubishi Electric,    “Implicit Resource Allocation of ACK/NACK Signal in E-UTRA Uplink,”    Report R1-072439, 3GPP TSG RAN WG1 Meeting #49, Kobe, Japan, May    7-11, 2007.-   Non-Patent Document 2: Nokia Siemens Networks, Nokia, “Multiplexing    capability of CQIs and ACK/NACKs form different UEs,” Report    R1-72315, 3GPP TSG RAN WG1 Meeting #49, Kobe, Japan, May 7-11, 2007.-   Non-Patent Document 3: 3GPP TS 36.211 V8.0.0, “Physical Channels and    Modulation (Release 8),” September 2007.

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

An example case will be described below where the constellation shown inFIG. 3 is used to modulate a response signal. Also, an example case willbe described below where one mobile station #1 transmits a responsesignal using PUCCH #1 (in FIG. 2) and another mobile station #2transmits a response signal using PUCCH #0 (in FIG. 2), In this case,the base station performs the above-described correlation processing todistinguish between the response signal from mobile station #1 and theresponse signal from mobile station #2. At this time, components of theresponse signal from mobile station #2 may leak in the correlationoutput to receive the response signal of mobile station #1, andinterfere with the response signal of mobile station #1.

Then, when mobile station #1 and mobile station #2 both transmit an ACKand the base station receives the response signal from mobile station#1, interference given from the response signal of mobile station #2 tothe response signal of mobile station #1 is as follows.

That is, when the ACK and reference signal transmitted from mobilestation #1 are received by the base station via a channel, in the basestation, a response signal represented by (−1−j)h1/√2 and a referencesignal represented by (1+j)h1/√2 are found as a correlation output ofmobile station #1. Here, h1 is an effective channel in a case where thesignals from mobile station #1 pass a channel between mobile station #1and the base station, and are found, as a correlation output, in thedetection window for mobile station #1 in the base station.

Also, when the ACK and reference signal transmitted from mobile station#2 are received by the base station via a channel, in the base station,the component represented by (−1−j)h2/√2 is found as interference to theresponse signal of mobile station #1 and the component represented by(1+j)h2/≈2 is found as interference to the reference signal of mobilestation #1 in the correlation output of mobile station #1. Here, h2 isan effective channel in a case where the signals from mobile station #2pass the channel between mobile station #2 and the base station, andleak, as the correlation output, in the detection window for mobilestation #1 in the base station.

When there is little delay on a channel and no transmission timingdifference at a mobile station, such a leak does not occur. But,depending on conditions, h2 may be non-negligibly high for h1.Therefore, when an ACK from mobile station #1 and an ACK from mobilestation #2 are code-multiplexed, in the base station, a response signalrepresented by (−1−j)(h1+h2)/√2 and a reference signal represented by(1+j)(h1+h2)/√2 are found in the correlation output of mobile station#1.

Therefore, the interference component given from the ACK of mobilestation #2 to the ACK of mobile station #1 (i.e., the Euclidean distancefrom (−1−j)/√2) by the synchronous detection in the base station, isrepresented by equation 1. That is, when both mobile station #1 andmobile station #2 transmit an ACK, there is no inter-code interferencebetween the ACK of mobile station #1 and the ACK of mobile station #2.

$\begin{matrix}{{\frac{\left( {1 + j} \right)}{\sqrt{2}}\left( {{- 1} - \frac{{- h_{1}} - h_{2}}{h_{1} + h_{2}}} \right)} = 0} & \left( {{Equation}\mspace{14mu} 1} \right)\end{matrix}$

Also, when mobile station #1 transmits a NACK, mobile station #2transmits an ACK and the base station receives the response signal frommobile station #1, interference from the response signal of mobilestation #2 to the response signal #1 is as follows.

That is, when the NACK and reference signal transmitted from mobilestation #1 are received by the base station via a channel, in the basestation, a response signal represented by (1+j)h1/√2 and a referencesignal represented by (1+j)h1/√2 are found as a correlation output ofmobile station #1.

Also, when the ACK and reference signal transmitted from mobile station#2 are received by the base station via a channel, in the base station,the component represented by (−1−j)h2/√2 is found as interference to theresponse signal of mobile station #1 and the component represented by(1+j)h2/√2 is found as interference to the reference signal of mobilestation #1 in the correlation output of mobile station #1.

Therefore, when the NACK from mobile station #1 and the ACK from mobilestation #2 are code-multiplexed, in the base station, a response signalrepresented by (1+j)(h1−h2)/√2 and a reference signal represented by(1+j)(h1+h2)/√2 are found in the correlation output of mobile station#1.

Therefore, the interference component given from the ACK of mobilestation #2 to the NACK of mobile station #1 (i.e., the Euclideandistance from (1+j)/√2) by the synchronous detection in the basestation, is represented by equation 2. That is, when mobile station #1transmits a NACK and mobile station #2 transmits an ACK, significantinter-code interference may be given from the ACK of mobile station #2to the NACK of mobile station #1.

$\begin{matrix}{{\frac{\left( {1 + j} \right)}{\sqrt{2}}\left( {1 - \frac{h_{1} - h_{2}}{h_{1} + h_{2}}} \right)} = {\frac{\left( {1 + j} \right)}{\sqrt{2}}\left( \frac{2h_{2}}{h_{1} + h_{2}} \right)}} & \left( {{Equation}\mspace{14mu} 2} \right)\end{matrix}$

Similarly, when mobile station #1 and mobile station #2 both transmit aNACK signal, as shown in equation 3, inter-code interference does notoccur between the NACK of mobile station #1 and the NACK of mobilestation #2. Also, when mobile station #1 transmits an ACK and mobilestation #2 transmits a NACK, as shown in equation 4, significantinter-code interference may be given from the NACK of mobile station #2to the ACK of mobile station #1.

$\begin{matrix}{{\frac{\left( {1 + j} \right)}{\sqrt{2}}\left( {1 - \frac{h_{1} + h_{2}}{h_{1} + h_{2}}} \right)} = 0} & \left( {{Equation}\mspace{14mu} 3} \right) \\{{\frac{\left( {1 + j} \right)}{\sqrt{2}}\left( {{- 1} - \frac{{- h_{1}} + h_{2}}{h_{1} + h_{2}}} \right)} = {\frac{\left( {1 + j} \right)}{\sqrt{2}}\left( \frac{{- 2}h_{2}}{h_{1} + h_{2}} \right)}} & \left( {{Equation}\mspace{14mu} 4} \right)\end{matrix}$

Here, while unnecessary retransmission of downlink data is performed inthe case where the base station receives an ACK from a mobile station asa NACK by mistake, necessary retransmission of downlink data is notperformed in the case where the base station receives a NACK from amobile station as an ACK by mistake. That is, in the latter case, themobile station needs to wait for retransmission control in a higherlayer than the base station to acquire desired downlink data, and, as aresult, downlink data transmission is delayed significantly. Taking intoaccount these results caused by reception error of response signals,3GPP-LTE defines the target ACK error rate to be approximately 1%, whiledefining the target NACK error rate to be approximately 0.01%. That is,there is a demand to decrease the NACK error rate sufficiently.

Here, taking into account that ARQ is applied to downlink data, 3GPP-LTEdefines approximately 1 to 10% of the target error rate per downlinkdata transmission. That is, in ARQ of downlink data, the ACK occurrencerate is significantly higher than the NACK occurrence rate. For example,in a mobile communication system in which the target error rate perdownlink data transmission is set to 10%, the ACK occurrence rate is90%, while the NACK occurrence rate is 10%. Therefore, in the aboveexample, there is a high possibility that a response signal of mobilestation #2 that interferes with a response signal of mobile station #1is an ACK. That is, there is a high possibility that, when mobilestation #1 transmits a NACK, significant inter-code interference(represented by equation 2) is given from a response signal of mobilestation #2 to this NACK, while there is a low possibility that, whenmobile station #1 transmits an ACK, significant inter-code interference(represented by equation 4) is given from a response signal of mobilestation #2 to this ACK. That is, there is a possibility that a NACK ismore influenced by interference than an ACK. Consequently, thepossibility of an increased error rate by interference becomes larger ina NACK than an ACK.

Therefore, there is a strong demand for a technique of preventing anincreased NACK error rate due to inter-code interference from an ACK andimproving the error rate performance of a NACK compared to the priorart, in the case where a plurality of response signals from a pluralityof mobile stations are code-multiplexed.

It is therefore an object of the present invention to provide a radiocommunication apparatus and constellation control method for improvingthe error rate performance compared to the prior art.

Means for Solving the Problem

The radio communication apparatus of the present invention employs aconfiguration having: a first spreading section that performs firstspreading of a response signal using one of a plurality of firstsequences that can be separated from each other because of differentcyclic shift values; a second spreading section that performs secondspreading of the response signal subjected to the first spreading usingone of a plurality of second sequences that are orthogonal to eachother; and an inverting section that, with reference to a firstconstellation of a first response signal group formed with responsesignals subject to the first spreading by a part of the plurality offirst sequences, inverts a second constellation of a second responsesignal group formed with response signals subject to the first spreadingby other first sequences than the part of the plurality of firstsequences.

The constellation control method of the present invention includes: afirst spreading step of performing first spreading of a response signalusing one of a plurality of first sequences that can be separated fromeach other because of different cyclic shift values; a second spreadingstep of performing second spreading of the response signal subjected tothe first spreading using one of a plurality of second sequences thatare orthogonal to each other; and an inverting step of, with referenceto a first constellation of a first response signal group formed withresponse signals subject to the first spreading by a part of theplurality of first sequences, inverting a second constellation of asecond response signal group formed with response signals subject to thefirst spreading by other first sequences than the part of the pluralityof first sequences.

Advantageous Effect of Invention

According to the present invention, it is possible to improve the errorrate performance of a NACK compared to the prior art.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing a spreading method of a response signal andreference signal (prior art);

FIG. 2 is a diagram showing the definition of PUCCH (prior art);

FIG. 3 illustrates a BPSK constellation (prior art);

FIG. 4 illustrates a QPSK constellation (prior art);

FIG. 5 is a block diagram showing the configuration of a base stationaccording to Embodiment 1 of the present invention;

FIG. 6 is a block diagram showing the configuration of a mobile stationaccording to Embodiment 1 of the present invention;

FIG. 7 is a diagram showing a constellation change according toEmbodiment 1 of the present invention;

FIG. 8 illustrates a BPSK constellation according to Embodiment 1 of thepresent invention;

FIG. 9 illustrates a QPSK constellation according to Embodiment 1 of thepresent invention;

FIG. 10 is a diagram showing scrambling processing according toEmbodiment 1 of the present invention;

FIG. 11 is a diagram showing a constellation change according toEmbodiment 3 of the present invention;

FIG. 12 is a block diagram showing the configuration of a mobile stationaccording to Embodiment 4 of the present invention;

FIG. 13 is a diagram showing scrambling processing according toEmbodiment 5 of the present invention;

FIG. 14 is a block diagram showing the configuration of a mobile stationaccording to Embodiment 5 of the present invention; and

FIG. 15 is a diagram showing a constellation change according toEmbodiment 6 of the present invention.

BEST MODE OF EMBODIMENTS OF THE INVENTION

Embodiments of the present invention will be explained below in detailwith reference to the accompanying drawings.

Embodiment 1

FIG. 5 illustrates the configuration of base station 100 according tothe present embodiment, and FIG. 6 illustrates the configuration ofmobile station 200 according to the present embodiment.

Here, to avoid complicated explanation, FIG. 5 illustrates componentsassociated with transmission of downlink data and components associatedwith reception of uplink response signals to the downlink data, whichare closely related to the present invention, and illustration andexplanation of the components associated with reception of uplink datawill be omitted. Similarly, FIG. 6 illustrates components associatedwith reception of downlink data and components associated withtransmission of uplink response signals to the downlink data, which areclosely related to the present invention, and illustration andexplanation of the components associated with transmission of uplinkdata will be omitted.

Also, a case will be described with the following explanation, where ZACsequences are used in first spreading and block-wise spreading codesequences are used in second spreading. Here, for first spreading, it isequally possible to use sequences, which can be separated from eachother because of different cyclic shift values, other than ZACsequences. For example, for first spreading, it is possible to use a GCL(Generated Chip like) sequence, CAZAC (Constant Amplitude Zero AutoCorrelation) sequence, ZC (Zadoff-Chu) sequence or PN sequence such asan M sequence and orthogonal Gold code sequence. Also, as block-wisespreading code sequences for second spreading, it is possible to use anysequences as long as these sequences are orthogonal or substantiallyorthogonal to each other. For example, it is possible to use Walshsequences or Fourier sequences as block-wise spreading code sequencesfor second spreading.

Also, in the following explanation, twelve ZAC sequences with a sequencelength of 12 and of cyclic shift values “0” to “11” are referred to as“ZAC #0” to “ZAC #11,” and three block-wise spreading code sequenceswith a sequence length of 4 and of sequence numbers “0” to “2” arereferred to as “BW #0” to “BW #2.” Here, the present invention is notlimited to these sequence lengths.

Also, in the following explanation, the PUCCH numbers are determined bythe cyclic shift values of ZAC sequences and the sequence numbers ofblock-wise spreading code sequences. That is, a plurality of resourcesfor response signals are determined by ZAC #0 to ZAC #11, which can beseparated from each other because of different cyclic shift values, andBW #0 to BW #2, which are orthogonal to each other.

Also, in the following explanation, the CCE numbers and the PUCCHnumbers are associated on a one-to-one basis. That is, CCE #0 is mappedto PUCCH #0, CCE #1 is mapped to PUCCH #1, CCE #2 is mapped to PUCCH #2. . . , and so on.

In base station 100 shown in FIG. 5, control information generatingsection 101 and mapping section 104 receive as input a resourceallocation result of downlink data. Also, control information generatingsection 101 and encoding section 102 receive as input a coding rate ofcontrol information to report the resource allocation result of downlinkdata, on a per mobile station basis, as coding rate information. Here,in the same way as above, the coding rate of the control information isone of ⅔, ⅓, ⅙ and 1/12.

Control information generating section 101 generates control informationto report the resource allocation result, on a per mobile station basis,and outputs the control information to encoding section 102. Controlinformation, which is provided per mobile station, includes mobilestation ID information to indicate to which mobile station the controlinformation is directed. For example, control information includes, asmobile station ID information, CRC bits masked by the ID number of themobile station, to which control information is reported. Further,according to the coding rate information received as input, controlinformation generating section 101 allocates an L1/L2 CCH to each mobilestation based on the number of CCE's required to report the controlinformation, and outputs the CCE number corresponding to the allocatedL1/L2 CCH to mapping section 104. Here, in the same way as above, anL1/L2 CCH occupies one CCE when the coding rate of control informationis ⅔. Therefore, an L1/L2 CCH occupies two CCE's when the coding rate ofcontrol information is ⅓, an L1/L2 CCH occupies four CCE's when thecoding rate of control information is ⅙, and an L1/L2 CCH occupies eightCCE's when the coding rate of control information is 1/12. Also, in thesame way as above, when one L1/L2 CCH occupies a plurality of CCE's, theCCE's occupied by the L1/L2 CCH are consecutive.

Encoding section 102 encodes control information on a per mobile stationbasis according to the coding rate information received as input, andoutputs the encoded control information to modulating section 103.

Modulating section 103 modulates the encoded control information andoutputs the result to mapping section 104.

On the other hand, encoding section 105 encodes the transmission datafor each mobile station (i.e., downlink data) and outputs the encodedtransmission data to retransmission control section 106.

Upon initial transmission, retransmission control section 106 holds theencoded transmission data on a per mobile station basis and outputs thedata to modulating section 107. Retransmission control section 106 holdstransmission data until retransmission control section 106 receives asinput an ACK of each mobile station from deciding section 117. Further,upon receiving as input a NACK of each mobile station from decidingsection 117, that is, upon retransmission, retransmission controlsection 106 outputs the transmission data matching that NACK tomodulating section 107.

Modulating section 107 modulates the encoded transmission data receivedas input from retransmission control section 106, and outputs the resultto mapping section 104.

Upon transmission of control information, mapping section 104 maps thecontrol information received as input from modulating section 103 on aphysical resource based on the CCE number received as input from controlinformation generating section 101, and outputs the result to IFFTsection 108. That is, mapping section 104 maps control information onthe subcarrier corresponding to the CCE number in a plurality ofsubcarriers forming an orthogonal frequency division multiplexing (OFDM)symbol, on a per mobile station basis.

On the other hand, upon transmission of downlink data, mapping section104 maps the transmission data, which is provided on a per mobilestation basis, on a physical resource based on the resource allocationresult, and outputs the result to IFFT section 108. That is, based onthe resource allocation result, mapping section 104 maps transmissiondata on a subcarrier in a plurality of subcarriers comprised of an OFDMsymbol, on a per mobile station basis.

IFFT section 108 generates an OFDM symbol by performing an IFFT of aplurality of subcarriers on which control information or transmissiondata is mapped, and outputs the OFDM symbol to CP (Cyclic Prefix)attaching section 109.

CP attaching section 109 attaches the same signal as the signal at thetail end part of the OFDM symbol, to the head of the OFDM symbol as aCP.

Radio transmitting section 110 performs transmission processing such asdigital-to-analog (D/A) conversion, amplification and up-conversion onthe OFDM symbol with a CP and transmits the result from antenna 111 tomobile station 200 (in FIG. 6).

On the other hand, radio receiving section 112 receives a responsesignal or reference signal transmitted from mobile station 200 (in FIG.6), via antenna 111, and performs receiving processing such asdown-conversion and analog-to-digital (A/D) conversion on the responsesignal or reference signal.

CP removing section 113 removes the CP attached to the response signalor reference signal subjected to receiving processing.

Despreading section 114 despreads the response signal by a block-wisespreading code sequence that is used in second spreading in mobilestation 200, and outputs the despread response signal to correlationprocessing section 115. Similarly, despreading section 114 despreads thereference signal by an orthogonal sequence that is used to spread thereference signal in mobile station 200, and outputs the despreadreference signal to correlation processing section 115.

Correlation processing section 115 finds the correlation value betweenthe despread response signal, despread reference signal and ZAC sequencethat is used in first spreading in mobile station 200, and outputs thecorrelation value to descrambling section 116.

Descrambling section 116 descrambles the correlation value by thescrambling code associated with the cyclic shift value of the ZACsequence, and outputs the descrambled correlation value to decidingsection 117.

Deciding section 117 detects a response signal on a per mobile stationbasis, by detecting a correlation peak on a per mobile station basisusing detection windows. For example, upon detecting a correlation peakin the detection window for mobile station #1, deciding section 117detects a response signal from mobile station #1. Then, deciding section117 decides whether the detected response signal is an ACK or NACK bythe synchronous detection using the correlation value of the referencesignal, and outputs the ACK or NACK to retransmission control section106 on a per mobile station basis.

On the other hand, in mobile station 200 shown in FIG. 6, radioreceiving section 202 receives the OFDM symbol transmitted from basestation 100 (in FIG. 5), via antenna 201, and performs receivingprocessing such as down-conversion and A/D conversion on the OFDMsymbol.

CP removing section 203 removes the CP attached to the OFDM symbolsubjected to receiving processing.

FFT (Fast Fourier Transform) section 204 acquires control information ordownlink data mapped on a plurality of subcarriers by performing a FFTof the OFDM symbol, and outputs the control information or downlink datato extracting section 205.

Extracting section 205 and decoding section 207 receive as input codingrate information indicating the coding rate of the control information,that is, information indicating the number of CCE's occupied by an L1/L2CCH.

Upon reception of the control information, based on the coding rateinformation, extracting section 205 extracts the control informationfrom the plurality of subcarriers and outputs it to demodulating section206.

Demodulating section 206 demodulates the control information and outputsthe demodulated control information to decoding section 207.

Decoding section 207 decodes the control information based on the codingrate information received as input, and outputs the decoded controlinformation to deciding section 208.

On the other hand, upon receiving the downlink data, extracting section205 extracts the downlink data directed to the mobile station from theplurality of subcarriers, based on the resource allocation resultreceived as input from deciding section 208, and outputs the downlinkdata to demodulating section 210. This downlink data is demodulated indemodulating section 210, decoded in decoding section 211 and receivedas input in CRC section 212.

CRC section 212 performs an error detection of the decoded downlink datausing a CRC check, generates an ACK in the case of CRC=OK (i.e., when noerror is found) and a NACK in the case of CRC=NG (i.e., when error isfound), as a response signal, and outputs the generated response signalto modulating section 213. Further, in the case of CRC=OK (i.e., when noerror is found), CRC section 212 outputs the decoded downlink data asreceived data.

Deciding section 208 performs a blind detection of whether or not thecontrol information received as input from decoding section 207 isdirected to the mobile station. For example, deciding section 208decides that, if CRC=OK is found (i.e., if no error is found) as aresult of demasking CRC bits by the ID number of the mobile station, thecontrol information is directed to the mobile station. Further, decidingsection 208 outputs the control information for the mobile station, thatis, the resource allocation result of downlink data for the mobilestation, to extracting section 205.

Further, deciding section 208 decides a PUCCH to use to transmit aresponse signal from the mobile station, from the CCE number associatedwith subcarriers on which the control information directed to the mobilestation is mapped, and outputs the decision result (i.e., PUCCH number)to control section 209. For example, in the same way as above, when theCCE corresponding to subcarriers, on which control information directedto the mobile station is mapped, is CCE #0, deciding section 208 decidesPUCCH #0 associated with CCE #0 as the PUCCH for the mobile station.Also, for example, when CCE's corresponding to subcarriers on whichcontrol information directed to the mobile station is mapped are CCE #0to CCE #3, deciding section 208 decides PUCCH #0 associated with CCE #0,which is the smallest number in CCE #0 to CCE #3, as the PUCCH for themobile station, and, when CCE's corresponding to subcarriers on whichcontrol information directed to the mobile station is mapped are CCE #4to CCE #7, deciding section 208 decides PUCCH #4 associated with CCE #4,which is the smallest number in CCE #0 to CCE #3, as the PUCCH for themobile station.

Based on the PUCCH number received as input from deciding section 208,control section 209 controls the cyclic shift value of a ZAC sequencethat is used in first spreading in spreading section 215 and ablock-wise spreading code sequence that is used in second spreading inspreading section 218. That is, control section 209 selects a ZACsequence of the cyclic shift value corresponding to the PUCCH numberreceived as input from deciding section 208, amongst ZAC #0 to ZAC #11,and sets the selected ZAC sequence in spreading section 215, and selectsthe block-wise spreading code sequence corresponding to the PUCCH numberreceived as input from deciding section 208, amongst BW #0 to BW #2, andsets the selected block-wise spreading code sequence in spreadingsection 218. That is, control section 209 selects one of a plurality ofresources defined by ZAC #0 to ZAC #11 and BW #0 to BW #2. Also, controlsection 209 reports the selected ZAC sequence to scrambling section 214.

Further, control section 209 controls a block-wise spreading codesequence that is used in second spreading in spreading section 223. Thatis, control section 209 sets the block-wise spreading code sequencecorresponding to the PUCCH number received as input from decidingsection 208, in spreading section 223.

Modulating section 213 modulates the response signal received as inputfrom CRC section 212 and outputs the result to scrambling section 214.Modulation processing in modulating section 213 will be described laterin detail.

Scrambling section 214 multiplies the modulated response signal (i.e.,response symbol) by a scrambling code “1” or “−1” depending on the ZACsequence selected in control section 209, and outputs the responsesignal multiplied by the scrambling code to spreading section 215. Here,by multiplication of the scrambling code “−1,” the constellation of theresponse signal is rotated. That is, the ACK received as input frommodulating section 213 and multiplied by the scrambling code “−1” isallocated to the signal point of a NACK in the constellation used formodulation in modulating section 213, and the NACK received as inputfrom modulating section 213 and multiplied by the scrambling code “−1”is allocated to the signal point of an ACK in the constellation used formodulation in modulating section 213. Thus, scrambling section 214functions as a rotation means to rotate the constellation of a responsesignal. Scrambling processing in scrambling section 214 will bedescribed later in detail.

Spreading section 215 performs first spreading of the response signaland reference signal (i.e., reference symbol) by the ZAC sequence set incontrol section 209, and outputs the response signal subjected to firstspreading to IFFT section 216 and the reference signal subjected tofirst spreading to IFFT section 221.

IFFT section 216 performs an IFFT of the response signal subjected tofirst spreading, and outputs the response signal subjected to an IFFT toCP attaching section 217.

CP attaching section 217 attaches the same signal as the signal at thetail end part of the response signal subjected to an IFFT, to the headof the response signal as a CP.

Spreading section 218 performs second spreading of the response signalwith a CP by the block-wise spreading code sequence set in controlsection 209, and outputs the response signal subjected to secondspreading, to multiplexing section 219.

IFFT section 221 performs an IFFT of the reference signal subjected tofirst spreading, and outputs the reference signal subjected to an IFFTto CP attaching section 222.

CP attaching section 222 attaches the same signal as the signal at thetail end part of the reference signal subjected to an IFFT, to the headof the reference signal.

Spreading section 223 performs second spreading of the reference signalwith a CP by the block-wise spreading code sequence set in controlsection 209, and outputs the reference signal subjected to secondspreading, to multiplexing section 219.

Multiplexing section 219 time-multiplexes the response signal subjectedto second spreading and the reference signal subjected to secondspreading in one slot, and outputs the result to radio transmittingsection 220.

Radio transmitting section 220 performs transmission processing such asD/A conversion, amplification and up-conversion on the response signalsubjected to second spreading or the reference signal subjected tosecond spreading, and transmits the resulting signal from antenna 201 tobase station 100 (in FIG. 5).

Next, modulation processing in modulating section 213 and scramblingprocessing in scrambling section 214 will be explained in detail.

In a plurality of response signals subject to second spreading by thesame block-wise spreading code sequence, inter-code interference on thecyclic shift axis is the largest between the response signals that arelocated on the closest positions to each other on the cyclic shift axis.For example, in six response signals subject to second spreading by BW#0 in FIG. 2, the response signal that is transmitted using PUCCH #1 issubject to the largest interference from the response signal that istransmitted using PUCCH #0 and the response signal that is transmittedusing PUCCH #2.

Also, the ACK occurrence rate is significantly higher than the NACKoccurrence rate, and, consequently, when a NACK is transmitted using anarbitrary PUCCH, there is a high possibility that a response signal thatinterferes with the PUCCH is an ACK. Therefore, to improve the errorrate performance of a NACK, it is important to reduce interference froman ACK.

Therefore, with the present embodiment, as shown in FIG. 7, theconstellation of each response signal is inverted by rotating theconstellation of each constellation by 180 degrees on the cyclic shiftaxis.

To be more specific, referring to six response signals subject to secondspreading by BW #0 in FIG. 7, the constellation acquired by invertingthe constellation of a response signal that is transmitted using PUCCH#0, is used as the constellation of a response signal that istransmitted using PUCCH #1, and the constellation acquired by invertingthe constellation of the response signal that is transmitted using PUCCH#1, is used as the constellation of a response signal that istransmitted using PUCCH #2. The same applies to PUCCH #2 to PUCCH #5.For example, when the modulation scheme of response signals is BPSK,constellation #1 of PUCCH #0, PUCCH #2 and PUCCH #4 is as shown in FIG.3, while constellation #2 of PUCCH #1, PUCCH #3 and PUCCH #5 is as shownin FIG. 8. Also, for example, when the modulation scheme of responsesignals is QPSK, constellation #1 of PUCCH #0, PUCCH #2 and PUCCH #4 isas shown in FIG. 4, while constellation #2 of PUCCH #1, PUCCH #3 andPUCCH #5 is as shown in FIG. 9.

Thus, according to the present embodiment, in ZAC #0, ZAC #2, ZAC #4,ZAC #6, ZAC #8 and ZAC #10 that are used in first spreading of responsesignals subject to second spreading by BW #0, response signals subjectto first spreading by ZAC #0, ZAC #4 and ZAC #8 form the first responsesignal group, and response signals subject to first spreading by ZAC #2,ZAC #6 and ZAC #10 form the second response signal group. That is,according to the present embodiment, the response signals belonging tothe first response signal group and the response signals belonging tothe second response signal group are alternately allocated on the cyclicshift axis. Then, while the constellation of the first response signalgroup is constellation #1 (in FIG. 3 and FIG. 4), the constellation ofthe second response signal group is constellation #2 (in FIG. 8 and FIG.9). That is, according to the present embodiment, the constellation ofthe second response signal group is inverted with respect to theconstellation of the first response signal group.

Also, according to the present embodiment, as shown in FIG. 10, theinversion of constellation is performed by scrambling processing inscrambling section 214.

That is, when the modulation scheme of response signals is BPSK,modulating section 213 modulates the response signals usingconstellation #1 shown in FIG. 3. Therefore, the signal point of an ACKis (−1/√2, −1/√2), and the signal point of a NACK is (1/√2, 1/√2). Also,the signal point of a reference signal received as input from spreadingsection 215 is the same as the signal point of a NACK, (1/√2, 1/√2).

Then, in response signals subject to second spreading using BW #0,scrambling section 214 multiplies a response signal subject to firstspreading using ZAC #0, ZAC #4 or ZAC #8 by scrambling code “1,” andmultiplies a response signal subject to first spreading using ZAC #2,ZAC #6 or ZAC #10 by scrambling code “−1.” Therefore, for the responsesignal subject to first spreading by ZAC #0, ZAC #4 or ZAC #8, thesignal point of an ACK is (−1/√2, −1/√2) and the signal point of a NACKis (1/√2, 1/√2). That is, the constellation of the response signalsubject to first spreading by ZAC #0, ZAC #4 or ZAC #8 is constellation#1 (in FIG. 3). On the other hand, for the response signal subject tofirst spreading by ZAC #2, ZAC #6 or ZAC #10, the signal point of an ACKis (1/√2, 1/√2) and the signal point of a NACK is (−1/√2, −1/√2). Thatis, the constellation of the response signal subject to first spreadingby ZAC #2, ZAC #6 or ZAC #10 is constellation #2 (in FIG. 8).

Thus, according to the present embodiment, by scrambling processing inscrambling section 214, the constellation of the second response signalgroup is inverted with respect to the constellation of the firstresponse signal group.

As described above, an example case will be described below where mobilestation #1 transmits a response signal using PUCCH #1 (in FIG. 7) andanother mobile station #2 transmits a response signal using PUCCH #0 (inFIG. 7). Therefore, constellation #2 (in FIG. 8) is used for theresponse signal of mobile station #1 and constellation #1 (in FIG. 3) isused for the response signal of mobile station #2.

When mobile station #1 and mobile station #2 both transmit an ACK andthe base station receives the response signal from mobile station #1,interference given from the response signal of mobile station #2 to theresponse signal of mobile station #1 is as follows.

That is, when the NACK and reference signal transmitted from mobilestation #1 are received by the base station via a channel, in the basestation, a response signal represented by (1+j)h1/√2 and a referencesignal represented by (1+j)h1/√2 are found as a correlation output ofmobile station #1.

Also, when the ACK and reference signal transmitted from mobile station#2 are received by the base station via a channel, in the base station,the component represented by (−1−j)h2/√2 is found as interference to theresponse signal of mobile station #1 and the component represented by(1+j)h2/√2 is found as interference to the reference signal of mobilestation #1 in the correlation output of mobile station #1.

Therefore, when the ACK from mobile station #1 and the ACK from mobilestation #2 are code-multiplexed, in the base station, a response signalrepresented by (1+j)(h1−h2)/√2 and a reference signal represented by(1+j)(h1+h2)/√2 are found in the correlation output of mobile station#1.

Therefore, the interference component given from the ACK of mobilestation #2 to the NACK of mobile station #1 (i.e., the Euclideandistance from (1+j)/√2) by the synchronous detection in the basestation, is represented by equation 2. That is, when both mobile station#1 and mobile station #2 transmit an ACK, there is no inter-codeinterference between the ACK of mobile station #1 and the ACK of mobilestation #2.

Also, when mobile station #1 transmits a NACK, mobile station #2transmits an ACK and the base station receives the response signal frommobile station #1, interference given from the response signal of mobilestation #2 to the response signal of mobile station #1 is as follows.

That is, when the NACK and reference signal transmitted from mobilestation #1 are received by the base station via a channel, in the basestation, a response signal represented by (1−j)h1/√2 and a referencesignal represented by (1+j)h1/√2 are found as a correlation output ofmobile station #1.

Also, when the ACK and reference signal transmitted from mobile station#2 are received by the base station via a channel, in the base station,the component represented by (−1−j)h2/√2 is found as interference to theresponse signal of mobile station #1 and the component represented by(1+j)h2/√2 is found as interference to the reference signal of mobilestation #1 in the correlation output of mobile station #1.

Therefore, when an ACK from mobile station #1 and an ACK from mobilestation #2 are code-multiplexed, in the base station, a response signalrepresented by (−1−j)(h1+h2)/√2 and a reference signal represented by(1+j)(h1+h2)/√2 are found in the correlation output of mobile station#1.

Therefore, the interference component given from the ACK of mobilestation #2 to the ACK of mobile station #1 (i.e., the Euclidean distancefrom (−1−j)/√2) by the synchronous detection in the base station, isrepresented by equation 1. That is, according to the present embodiment,when mobile station #1 transmits a NACK and mobile station #2 transmitsan ACK, inter-code interference does not occur between the NACK ofmobile station #1 and the ACK of mobile station #2.

Similarly, according to the present embodiment, when mobile station #1and mobile station #2 both transmit a NACK, as shown in equation 4,significant inter-code interference may be given from the NACK of mobilestation #2 and the NACK of mobile station #1. Also, according to thepresent embodiment, when mobile station #1 transmits an ACK and mobilestation #2 transmits a NACK, as shown in equation 3 inter-codeinterference does not occur between the ACK of mobile station #1 to theNACK of mobile station #2.

Thus, the present embodiment makes interference given from a NACK to anACK zero by inverting the constellation of each response signal on thecyclic shift axis.

Also, as described above, the ACK occurrence rate is significantlyhigher than the NACK occurrence rate, and, consequently, when a responsesignal of mobile station #1 is a NACK, there is an extremely lowpossibility that a response signal of mobile station #2 is also a NACK.That is, there is an extremely low possibility that a response signalthat interferes with a NACK is a NACK. Therefore, there is littlepossibility that an increased NACK error rate is caused by interferencebetween NACK's. That is, the interference component of equation 4 thatoccurs in the present embodiment is not a problem.

Also, according to the present embodiment, there is a large possibilitythat the interference shown in equation 2 occurs between ACK's. However,as described above, if a base station receives an ACK from a mobilestation as a NACK by mistake, unnecessary retransmission of downlinkdata is performed, and, consequently, there is little influence on thecommunication system due to an increased error rate of an ACK.

Thus, according to the present embodiment, the constellation of eachresponse signal is inverted on the cyclic shift axis, so that it ispossible to prevent an increased NACK error rate due to inter-codeinterference from an ACK and improve the error rate performance of aNACK compared to the prior art.

Embodiment 2

With the present embodiment, Embodiment 1 is implemented only in aspecific slot among a plurality of slots forming one subframe.

For example, when one subframe is formed with two slots of slot #0 andslot #1, the constellation of the first response signal group and theconstellation of the second response signal group are both constellation#1 (in FIG. 3 and FIG. 4) in slot #0, while, as in Embodiment 1, theconstellation of the first response signal group is constellation #1 (inFIG. 3 and FIG. 4) and the constellation of the second response signalgroup is constellation #2 (in FIG. 8 and FIG. 9) in slot #1. By thismeans, it is possible to improve the error rate performance of an ACK inslot #0.

Therefore, according to the present embodiment, by adjusting the numberof specific slots in which a constellation is inverted (as in Embodiment1), it is possible to easily adjust both the ACK error rate and the NACKerror rate according to the target error rate.

Also, according to the present embodiment, a modulation scheme used inslot #0 and a modulation scheme used in slot #1 may be different fromeach other. For example, it is possible to use QPSK in slot #1 when BPSKis used in slot #0, or use BPSK in slot #1 when QPSK is used in slot #0.

Embodiment 3

With the present embodiment, for example, while the constellation isinverted in cell #1 as shown in FIG. 7, the constellation is inverted incell #2 adjacent to cell #1 as shown in FIG. 11. Therefore, for example,referring to PUCCH #1, while constellation #2 (in FIG. 8 and FIG. 9) isused for PUCCH #1 in cell #1, constellation #1 (in FIG. 3 and FIG. 4) isused for PUCCH #1 in cell #2. Similarly, referring to PUCCH #2, whileconstellation #1 (in FIG. 3 and FIG. 4) is used for PUCCH #2 in cell #1,constellation #2 (in FIG. 8 and FIG. 9) is used for PUCCH #2 in cell #2.

That is, with the present invention, further to Embodiment 1, betweentwo adjacent cells, the constellation of one of two response signalssubject to first spreading by ZAC sequences of the same cyclic shiftvalue, is inverted with respect to the constellation of the otherresponse signal.

By this means, between a plurality of adjacent cells, it is possible torandomize interference between a plurality of response signals subjectto first spreading by ZAC sequences of the same cyclic shift value. Thatis, according to the present embodiment, it is possible to randomize andreduce inter-cell interference between response signals.

Embodiment 4

With the present embodiment, the constellation is inverted uponmodulation of response signals.

FIG. 12 illustrates the configuration of mobile station 400 according tothe present embodiment. Here, in FIG. 12, the same components as in FIG.6 (Embodiment 1) will be assigned the same reference numerals and theirexplanation will be omitted.

In mobile station 400, a ZAC sequence selected in control section 209 isreported to modulating section 401.

Then, in response signals subject to second spreading using BW #0 shownin FIG. 7, modulating section 401 modulates a response signal subject tofirst spreading by ZAC #0, ZAC #4 or ZAC #8 (i.e., first response signalgroup) using constellation #1 (in FIG. 3 and FIG. 4), and modulates aresponse signal subject to first spreading by ZAC #2, ZAC #6 or ZAC #10(i.e., second response signal group) using constellation #2 (in FIG. 8and FIG. 9).

Thus, according to the present embodiment, upon modulation processing inmodulating section 401, the constellation of the second response signalgroup is inverted with respect to the constellation of the firstresponse signal group. That is, according to the present embodiment,modulating section 401 functions as a modulating means that modulates aresponse signal and as an inverting means that inverts the constellationof the response signal. Therefore, the present embodiment does notrequire scrambling section 214 (in FIG. 6) and descrambling section 116(in FIG. 5) in Embodiment 1.

Thus, by performing inversion processing of the constellation inmodulating section 401 instead of scrambling section 214, it is possibleto achieve the same effect as in Embodiment 1.

Embodiment 5

Embodiments 1 to 4 invert the constellation of a response signal withoutchanging the constellation of a reference signal. By contrast with this,as shown in FIG. 13, the present embodiment inverts the constellation ofa reference signal without changing the constellation of a responsesignal.

FIG. 14 illustrates the configuration of mobile station 600 according tothe present embodiment. Here, in FIG. 14, the same components as in FIG.6 (Embodiment 1) will be assigned the same reference numerals and theirexplanation will be omitted.

In mobile station 600, when the modulation scheme of response signals isBPSK, scrambling section 214 multiplies a reference signal subject tofirst spreading using ZAC #0, ZAC #4 or ZAC #8 by “1,” and multiplies areference signal subject to first spreading using ZAC #2, ZAC #6 or ZAC#10 by “−1.” Therefore, the signal point of a reference signal subjectto first spreading by ZAC #0, ZAC #4 or ZAC #8 is (1/√2, 1/√2), and thesignal point of a reference signal subject to first spreading by ZAC #2,ZAC #6 or ZAC #10 is (1/√2, −1/√2).

Thus, by scrambling processing in scrambling section 214, the presentembodiment inverts the constellation of a reference signal for thesecond response signal group with respect to the constellation of areference signal for the first response signal group.

Thus, by performing inversion processing of the constellation of areference signal in scrambling section 214, it is equally possible toachieve the same effect as in Embodiment 1.

Embodiment 6

If there is a large difference of received power between responsesignals from a plurality of mobile stations at a base station, responsesignals of higher received power may interfere with response signals oflower received power. For example, in response signals subject to secondspreading using BW #0 shown in FIG. 15, when the received power of aresponse signal that is transmitted using PUCCH #0 and the receivedpower of a response signal that is transmitted using PUCCH #3 arehigher, and the received power of response signals that are transmittedusing the other PUCCH's is lower, the response signal that istransmitted using PUCCH #0 and the response signal that is transmittedusing PUCCH #3 give the largest interference to response signals thatare transmitted using the other PUCCH's.

Therefore, in this case, in ZAC #0, ZAC #2, ZAC #4, ZAC #6, ZAC #8 andZAC #10 that are used in first spreading of response signals subject tosecond spreading using BW #0, the response signals subject to firstspreading by ZAC #0 and ZAC #6 form the first response signal group, andthe response signals subject to first spreading by ZAC #2, ZAC #4, ZAC#8 and ZAC #10 form the second response signal group. Then, while theconstellation of the first response signal group is constellation #1 (inFIG. 3 and FIG. 4), the constellation of the second response signalgroup is constellation #2 (in FIG. 8 and FIG. 9). That is, the presentembodiment inverts the constellation of the second response signal groupof lower received power with respect to the constellation of the firstresponse signal group of higher received power.

Thus, according to the present embodiment, by inverting theconstellation of a signal of lower received power with respect to theconstellation of a response signal of higher received power on thecyclic shift axis, it is possible to prevent an increased NACK errorrate by inter-code interference from an ACK due to the received powerdifference, and, as in Embodiment 1, improve the error rate performanceof a NACK compared to the prior art.

Embodiments of the present invention have been described above.

Also, a PUCCH used in the above-described embodiments is a channel tofeed back an ACK or NACK, and therefore may be referred to as an“ACK/NACK channel.”

Also, it is possible to implement the present invention as describedabove, even when other control information than a response signal is fedback.

Also, a mobile station may be referred to as a “UE,” “MT,” “MS” and “STA(station).” Also, a base station may be referred to as a “node B, “BS”or “AP.” Also, a subcarrier may be referred to as a “tone.” Also, a CPmay be referred to as a “GI (Guard Interval).”

Also, the method of error detection is not limited to CRC check.

Also, a method of performing transformation between the frequency domainand the time domain is not limited to IFFT and FFT.

Also, a case has been described with the above-described embodimentswhere the present invention is applied to mobile stations. Here, thepresent invention is also applicable to a fixed radio communicationterminal apparatus in a stationary state and a radio communication relaystation apparatus that performs the same operations with a base stationas a mobile station. That is, the present invention is applicable to allradio communication apparatuses.

Although a case has been described with the above embodiments as anexample where the present invention is implemented with hardware, thepresent invention can be implemented with software.

Furthermore, each function block employed in the description of each ofthe aforementioned embodiments may typically be implemented as an LSIconstituted by an integrated circuit. These may be individual chips orpartially or totally contained on a single chip. “LSI” is adopted herebut this may also be referred to as “IC,” “system LSI,” “super LSI, or“ultra LSI” depending on differing extents of integration.

Further, the method of circuit integration is not limited to LSI's, andimplementation using dedicated circuitry or general purpose processorsis also possible. After LSI manufacture, utilization of an FPGA (FieldProgrammable Gate Array) or a reconfigurable processor where connectionsand settings of circuit cells in an LSI can be reconfigured is alsopossible.

Further, if integrated circuit technology comes out to replace LSI's asa result of the advancement of semiconductor technology or a derivativeother technology, it is naturally also possible to carry out functionblock integration using this technology. Application of biotechnology isalso possible.

The disclosure of Japanese Patent Application No. 2007-280795, filed onOct. 29, 2007, including the specification, drawings and abstract, isincorporated herein by reference in its entirety.

INDUSTRIAL APPLICABILITY

The present invention is applicable to, for example, mobilecommunication systems.

The various embodiments described above can be combined to providefurther embodiments. All of the U.S. patents, U.S. patent applicationpublications, U.S. patent applications, foreign patents, foreign patentapplications and non-patent publications referred to in thisspecification and/or listed in the Application Data Sheet areincorporated herein by reference, in their entirety. Aspects of theembodiments can be modified, if necessary to employ concepts of thevarious patents, applications and publications to provide yet furtherembodiments.

The invention claimed is:
 1. A radio communication apparatus comprisinga processor configured: to spread transmission signals using a pluralityof sequences that can be separated from each other because of differentcyclic shift values; to use received power at a receiver as a basis forallocating transmission signals to a first signal group or to a secondsignal group, the first signal group comprising at least a transmissionsignal which is spread using a first sequence of the plurality ofsequences and the second signal group comprising transmission signalswhich are spread using other sequences of the plurality of sequences,the first signal group and the second signal group having differentreceived power at the receiver; and to invert a constellation of thesecond signal group with respect to a constellation of the first signalgroup for transmission to the receiver.
 2. The radio communicationapparatus of claim 1, further comprising a transmitter configured totransmit the transmission signals to the receiver.
 3. The radiocommunication apparatus of claim 1, wherein the transmission signalscomprise a response signal.
 4. The radio communication apparatus ofclaim 3, wherein the processor is configured to invert the constellationof the second signal group with respect to the constellation of thefirst signal group to prevent an increased negative acknowledgement(NACK) error rate by inter-code interference from an acknowledgement(ACK).
 5. The radio communication apparatus of claim 1, wherein theplurality of sequences comprise Zero Auto Correlation (ZAC) sequences.6. The radio communication apparatus of claim 1, wherein the radiocommunication apparatus comprises a mobile station.
 7. A method ofoperating radio communication apparatus comprising: spreadingtransmission signals using a plurality of sequences that can beseparated from each other because of different cyclic shift values;using received power at a receiver as a basis for allocatingtransmission signals to a first signal group or to a second signalgroup, the first signal group comprising at least a transmission signalwhich is spread using a first sequence of the plurality of sequences anda second signal group comprising transmission signals which are spreadusing other sequences of the plurality of sequences, the first signalgroup and the second signal group having different received power at thereceiver; and inverting a constellation of the second signal group withrespect to a constellation of the first signal group for transmission tothe receiver.
 8. The method of claim 7, further comprising transmittingthe transmission signals to the receiver.
 9. The method of claim 7,wherein the transmission signals comprise a response signal.
 10. Themethod of claim 9, further comprising inverting the constellation of thesecond signal group with respect to the constellation of the firstsignal group to prevent an increased negative acknowledgement (NACK)error rate by inter-code interference from an acknowledgement (ACK). 11.The method of claim 7, wherein the plurality of sequences comprise ZeroAuto Correlation (ZAC) sequences.
 12. The method of claim 7, wherein theacts of spreading, forming, and inverting are performed by a processorof the radio communication apparatus.
 13. The method of claim 7, whereinthe acts of spreading, forming, and inverting are performed by aprocessor of a mobile station.